There is an undocumented option: MYSQLI_OPT_READ_TIMEOUT. This is similar to MYSQLI_OPT_CONNECT_TIMEOUT in theory, but has a slightly different application. Connection timeout only specifies the wait time for the initial TCP connection. Once that is created, the timeout no longer applies. Read timeout, however, is from the time the TCP connection is created until the first packet of actual data is received. There are instances where a TCP connection can be established, but the MySQL server stalls indefinitely, preventing execution from ever returning to PHP. Specifying a read timeout alleviates this condition, whereas connect timeout wouldn't.

If the MYSQLI_OPT_READ_TIMEOUT constant isn't defined, it is still supported on versions where that isn't the case. You can define it yourself in older PHP versions with the following code.

You can then use read timeout the same way you could a connect timeout as follows. Please note that since these are two different timeout values for two different parts of the entire connection process, the timeouts do stack (eg: 10 seconds connect timeout + 10 seconds read timeout = maximum possible timeout of 20 seconds)